Postural Orthostatic Tachycardia Syndrome (POTS) is characterized by an increase of heart rate of 30 beats per minute (40 bpm in patients aged 12-19 years) upon a postural change, combined with the presence of orthostatic symptoms. In addition to these criteria, recent studies have shown that POTS patients exhibit large low frequency ~0.1 Hz heart rate and blood pressure oscillations upon a postural change when compared to control subjects. Moreover, several studies have hypothesized that POTS patients express autoantibodies binding to beta_{1,2} and M_2 receptors. These receptors are abundant on the sinoatrial node, while \alpha_1 receptors are associated with smooth muscle cells. This study uses mathematical modeling to test if subjects expressing these antibodies experience augmented ~0.1 Hz oscillations. To do so, we develop a multiscale model using a systems level five-compartment cardiovascular model, a baroreflex control regulating heart rate, cardiac contractility, and vascular resistance in response to changes in blood pressure. Specific attention is paid to the control of heart rate achieved by adding a sinoatrial node cell model. We demonstrate that by changing receptor sensitivity we can predict ~0.1 Hz oscillations in POTS patients, Finally, we show that by varying system level model parameters we can simulate characteristic POTS phenotypes and study effects of POTS in patients with low blood volume, known to have more severe POTS symptoms.